Electroencephalography (EEG) is the recording of the brain's spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple electrodes placed on the scalp. Diagnostic applications generally focus on neural oscillations that can be observed in EEG signals.

EEG is most often used to diagnose Epilepsy, which causes obvious abnormalities in EEG readings. It is also used to diagnose Sleep Disorders,Coma, Encephalopathies, and Brain Death.

EEG used to be a first-line method of diagnosis for Tumors, Stroke and other Focal Brain Disorders, But this use has decreased with the advent of high-resolution anatomical imaging techniques such as MRI and CT.